In a gasoline engine, the vehicle is set in driving operation and/or the driving operation is maintained as the result of combustion of the supplied fuel-air mixture. The combustion of the fuel-air mixture is initiated by the ignition spark of a spark plug. The ignition spark forms a flame front which propagates in the entire combustion chamber, and the air-fuel mixture that is present is converted into kinetic energy during the combustion. For knocking combustions, a portion of the combustions proceed suddenly and cause a great pressure rise in the combustion chamber of the gasoline engine which generates a pressure wave that propagates and strikes the walls delimiting the combustion chamber, where the high-frequency oscillations are converted into structure-borne noise. These oscillations are detected by knock sensors (structure-borne noise sensors) and taken into account in controlling the gasoline engine by knock control in order to prevent engine damage. The gasoline engine is always operated at the knock limit in an efficiency-optimized manner. Damage to the gasoline engine as the result of the continually recurring knocking combustions is avoided with the aid of the knock control.
However, in addition to the described knocking combustions, auto-ignitions occur as the result of hot spots in the combustion chamber, oil droplets, or hot residual gas zones in the fuel-air mixture. Such auto-ignitions may appear as pre-ignitions before the ignition spark occurs, and as post-ignitions after the ignition spark occurs. One or multiple additional flame fronts arise in addition to the flame front induced by ignition sparks. These auto-ignitions are usually referred to as pre-ignitions, and increase the risk of knocking combustions in the end-gas zone. The structure-borne noise oscillations which occur are characterized by extreme pressure amplitudes, which may very quickly result in engine damage.
German Patent Application No. DE 696 28 770 T2 describes that such anomalous auto-ignitions may be recognized in that the amplitude of an auto-ignition is larger than a predefined threshold value, the auto-ignition being recognized in two steps: once after a first predetermined time period after the ignition has elapsed, and in a second step after a second predetermined time period, which is longer than the first predetermined time period, has elapsed. To minimize the auto-ignitions, after the anomalous auto-ignition has been identified, the amount of fuel injected is increased or decreased, or a throttle valve is closed. Determining the auto-ignitions requires a great expenditure of computing time, which delays a quick response to the anomalous auto-ignitions.